1. Field of the Invention
The present invention relates to a method and system for re-routing a call which has been routed from a calling party through a communication network to a destination, wherein the call needs to be relayed from the destination to another destination, as for example in case of a wrong destination such as a wrong message server.
2. Description of the Prior Art
Recently, the features offered by communication networks in connection with so-called value added services have remarkably increased. Among such features, a feature has been developed which permits a calling subscriber to leave a message on a message server for the called subscriber, in case the called subscriber cannot be reached. The called subscriber may then listen to the message which has been left at any later point of time. Thus, such a message server has a function of an answering machine provided at the communication network side.
According to the prior art, several related services have been proposed.
The U.S. Pat. No. 4,930,152 discloses a call return telephone service, wherein a list of the telephone numbers of calling subscribers is kept in a switch (exchange) of the network for the purpose of calling back previously calling subscribers. However, specific messages having a content defined by the calling subscriber cannot be stored for the called subscriber.
Furthermore, EP-A-0 795 992 discloses a method and apparatus for providing a prepaid return call in connection with a message server. The called subscriber as the recipient of messages stored in the message server is not enabled to initiate a listening operation for reading the contents of a message stored for him. Instead, the message server periodically tries to contact the called subscriber in order to deliver the stored message. Thus, the message may never be delivered to the called subscriber.
Additionally, EP-A-0 897 239 discloses a program-controlled communication system, having access to a voice mail server. According to this prior art, a called subscriber may retrieve messages intended for the subscriber from the voice mail server. A calling subscriber may then automatically be called back upon retrieval of the corresponding message. However, such a call back mechanism does not allow a direct call back from the called to the (previously) calling subscriber, since only pre-stored messages are exchanged with an interaction of the message service being involved between the called and the calling subscriber or vice versa.
To enhance the proposed call back mechanisms, a call drop-back function or mechanism has been proposed so as to enable a called subscriber to make a call back call to several different calling subscribers during a single message server session. To achieve this, required information is transmitted between the message server and the exchange or switching center in a call drop-back message using different parameters, that is a call drop-back type indicator indicating if a re-establishment of the listening call to the message server is needed after the call back call is terminated, a call drop-back release reason indicator indicating whether the call back call to the subscriber has been successful or not, and a message server session indicator containing a subscriber identification of the called subscriber and a message identification identifying the message listened to, so as to enable a resumption of the listening call after the call back call has been terminated.
The above call drop-back mechanism leads to the advantage that a called subscriber listening to recorded messages is enabled to carry on listening to his messages after a call back call to the subscriber who has left that message, without the need to make a new call to the message server afterwards. Thus, signaling load in the network can be reduced.
However, an initial direct routing to the right message server may not be possible for example when the subscriber is calling from abroad and the CLI (Calling Line Identification) is not available, or a subscriber not using the own mobile terminal uses a so-called “common access number” to access the message services, such that a HLR interrogation or enquiry for obtaining the subscriber identity is not possible.
In case a message server is accessed via an unstructured data service such as the USSD (Unstructured Supplementary Service Data) service, several message servers may be connected to the same USSD center (USSDC), such that it is quite possible that the call will be connected to a wrong message server.